Apparatus for pressure welding metal workpieces

ABSTRACT

A method and apparatus for pressure welding together novel aluminum or magnesium workpieces. Edges of workpieces to be pressure welded together are aligned with each other by abutment and one workpiece retracted from the other a predetermined distance to define an open channel between the edges. The workpiece edges are quickly heated to a temperature within the range of from about 200° to 900° F. by passing a uniform flow of heating gases through the channel such that the edge tip and sides of each workpiece are softened while the edge inner cores remain cooler and harder with their mechanical properties unaffected by the heat and the workpieces then moved into abutment with each other to close the channel and immediately pressed together under high pressure for expulsion of softened metal containing deleterious materials such as surface oxides and creation of a solid-phase weld bond between the relatively cool and hard inner cores. An air curtain can be provided to improve control of the heating of the workpieces and to enhance pressure welding together of workpieces of different gauges and of different metals, such as welding of aluminum to magnesium alloys.

This is a division of application Ser. No. 711,037 filed Aug. 2, 1976,now U.S. Pat. No. 4,094,453 issued June 13, 1978.

BACKGROUND OF THE INVENTION

This invention relates to pressure welding of metal workpieces and, moreparticularly, is directed to a method and apparatus for pressure weldingmetal workpieces of high strength aluminum or magnesium alloy and tonovel workpieces welded thereby.

The pressure welding of metals by cold welding and hot weldingtechniques is well known. Each technique has certain limitations in thatcold pressure welding requires a large amount of deformation andextremely high pressures to obtain a weld and, in many cases, it hasbeen found impossible to obtain welds at room temperature because ofexcessive cracking and insufficient flow of the metal. Hot pressurewelding of metals such as aluminum, on the other hand, normally isconducted at a temperature in excess of 900° F. with relatively littledeformation and upset. However, known hot pressure welding methods havethe inherent disadvantage of overaging, recrystallizing and annealingthe metals welded resulting in low joint efficiencies of about 30 to40%.

SUMMARY OF THE INVENTION

The method of the present invention differs from the aforesaid cold andhot pressure welding techniques in that only sufficient heat is providedto the welding operation to allow the metals to flow without crackingduring the welding process, without the harmful effects on the metals ofoveraging, recrystallization and annealing. Joint efficiencies in thewelding of aluminum and magnesium alloys of at least 90%, and often inexcess of 100%, can be obtained.

This invention relates to pressure welding of metal workpieces and, moreparticularly, is directed to a method and apparatus for pressure weldingmetal workpieces of high strength aluminum or magnesium alloy and tonovel workpieces welded thereby.

The pressure welding of metals by cold welding and hot weldingtechniques is well known. Each technique has certain limitations in thatcold pressure welding requires a large amount of deformation andextremely high pressures to obtain a weld and, in many cases, it hasbeen found impossible to obtain welds at room temperature because ofexcessive cracking and insufficient flow of the metal. Hot pressurewelding of metals such as aluminum, on the other hand, normally isconducted at a temperature in excess of 900° F. with relatively littledeformation and upset. However, known hot pressure welding methods havethe inherent disadvantage of overaging, recrystallizing and annealingthe metals welded resulting in low joint efficiencies of about 30 to40%.

The method of the present invention differs from the aforesaid cold andhot pressure welding techniques in that only sufficient heat is providedto the welding operation to allow the metals to flow without crackingduring the welding process, without the harmful effects on the metals ofoveraging, recrystallization and annealing. Joint efficiencies in thewelding of aluminum and magnesium alloys of at least 90%, and often inexcess of 100%, can be obtained.

United States patent application Ser. No. 679,307 discloses a method ofpressure welding aluminum and magnesium alloys at elevated temperaturesunder conditions which will enhance plastic flow of the metal during thewelding operation but which will preclude overaging, recrystallizationor partial annealing of the metal. The method of the present inventionconstitutes an improvement over the method taught in this co-pendingapplication.

U.S. Pat. No. 3,603,498 issued Sept. 7, 1971 is directed to a weldingmachine for pressure welding flat sheet metal workpieces together. Theapparatus of the present invention constitutes an improvement over thisstructure.

In general, the method of the invention comprises the steps ofjuxtaposing a longitudinal edge of a first workpiece gripped between apair of dies into substantially parallel spaced alignment with alongitudinal edge of a second workpiece gripped between a second pair ofdies, maintaining the longitudinal edge of the first workpiece betweenabout 1/32 to 1 inch away from the opposed longitudinal edge of thesecond workpiece so as to form an elongated open rectangular channeltherebetween, introducing a uniform stream of heated gases into theproximity of the opposed longitudinal edges and causing a portion ofsaid stream of heated gases to flow through said elongated openrectangular channel, maintaining the flow of heated gases through saidelongated open rectangular channel for a time sufficient to heat thesurfaces of said opposed edges to a temperature within the range of fromabout 200° to 900° F. and to form a core of relatively cooler and hardermaterial within each edge, eliminating said elongated open rectangularchannel by moving the longitudinal edges of said workpieces intoabutting relationship with each other to obviate the flow of said heatedgases therethrough, and immediately applying pressure to the abuttingheated longitudinal edges of said workpieces while they are at atemperature of between about 200° to 900° F. to create a solid-phaseweld bond between the cores and to upset a portion of heated adjacentsurfaces and cause heated metal to be substantially displaced out of theplane of said pressure welded interface.

More particularly, the method of the invention additionally comprisesjuxtaposing the longitudinal edges of the workpieces in opposedalignment with each other a substantially parallel, spaced distanceapart by abutting the said edges of the workpieces with each other andretracting one of said workpieces a desired predetermined distance,introducing a uniform stream of heated gases into the proximity of theopposed edges by feeding a combustible mixture of gases through aplurality of equispaced apertures positioned to one side of saidworkpieces adjacent to the spaced opposed edges, for heating of saidedges only when said rectangular channel is formed, and providing an aircurtain between said combustible mixture of gases and a die.

It is a principal object of the present invention to provide an improvedmethod of pressure welding metal workpieces by creating a solid-phaseweld bond which will provide a high degree of reliability and uniformityin weld strength and weld continuity.

The forging press of the present invention for joining two metalworkpieces comprises, in general, at least one pair of stationaryC-shaped metal plate frames arranged in a parallel side-by-sidespaced-apart relationship, a laterally movable C-shaped metal framemounted between each pair of stationary C-shaped metal plate frames, afirst pair of die holders associated with each pair of stationaryC-shaped metal plate frames adapted to grip a workpiece therebetween, atleast one of said die holders being mounted for movement in a verticaldirection relative to the other, a second pair of die holders associatedwith said laterally movable C-shaped metal frame adapted to grip aworkpiece therebetween, at least one of said die holders being mountedfor movement in a vertical direction relative to the other, means formoving said laterally movable C-shaped metal frame between saidstationary C-shaped metal plate frames whereby die holders associatedwith said laterally movable C-shaped metal frame can be moved towardsand away from the die holders associated with said stationary C-shapedmetal plate frames such that workpieces gripped therebetween can bespaced a fixed distance apart in alignment with each other prior toabutment of said workpieces for pressure welding and can be abuttedtogether at a pressure above the yield strength of the metal of theworkpieces at working temperatures sufficient to permit metal flow, andmeans for rapidly heating the opposed edges of said workpieces to auniform temperature within the range of from about 200° to about 900° F.while said workpieces are spaced a fixed distance apart immediatelyprior to abutment for pressure welding.

It is another important object of the present invention to provide animproved pressure welding apparatus which will permit rapid and reliableproduction of pressure welded products.

We have found that the configuration of the longitudinal edges of theworkpieces is critical to permit optimum weld efficiency with a minimumof heating time. Another object of the present invention is theprovision of novel workpiece configurations which are amenable topressure welding.

These and other objects of the invention and the manner in which theycan be attained will become apparent from the following detaileddescription of the drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a portion of the machine of the presentinvention showing the relative layout of component parts of the machine;

FIG. 2 is a side elevation, partly cut away, of the machine illustratedin FIG. 1;

FIG. 3 is a plan view of the machine illustrated in FIG. 1;

FIG. 4 is a front view of the machine illustrated in FIG. 1;

FIG. 5 is an enlarged fragmentary view of the die holders and dies ofthe machine of the present invention in their retracted, fully openedpositions, showing the heating manifold, taken along the line 5--5 ofFIG. 1;

FIG. 6 is an enlarged fragmentary view of the die holders with diesshown in FIG. 6 in a first position in which the workpieces are aligned,taken along the line 5--5 of FIG. 1;

FIG. 7 is an enlarged fragmentary view of the said die holders and diesin a second position in which the workpieces are retracted to form aheating channel;

FIG. 8 is an enlarged fragmentary view of the die holders and dies intheir final pressure welding position in which the workpieces arepressure welded together;

FIG. 9 is a cross-sectional view of a preferred configuration ofworkpieces used according to the method of the present invention;

FIG. 10 is a graphical presentation of the forging pressure, detentpressure, heat supply temperature and workpiece temperature during eachpressure welding cycle; and

FIG. 11 is a cross-sectional view of the workpiece after completion ofthe pressure welding cycle indicating the disposition of heatedworkpiece metal upset as flash.

With reference now to FIGS. 1-4, the forging press of the presentinvention comprises a plurality of stationary C-frames 10 arrangedparallel to each other a uniformly spaced distance apart by tie-bolts 12and spacers 14 located at the corners of the C-frames. A movable C-frame16 is mounted between each pair of adjacent stationary C-frames 10 forreciprocal sliding travel on pillow blocks 17 guided by alignment rods18 rigidly secured to spacer blocks 20 disposed between adjacentstationary C-frames 10.

This arrangement of the interconnected stationary frames 10 results in amodular type of machine which may be made any desired length by simplybolting together the desired number of stationary frames 10 and movableframes 16, the present embodiment showing six movable C-frames operatingin unison as will be described in detail hereinbelow.

With particular reference to FIG. 2, a plurality of sets of four dieholders 22, 24, 26 and 28 are positioned within the cavity defined bythe jaws of stationary and movable C-frames 10, 16. Die holders 22,24are mounted one above the other in stationary C-frames 10, die holders22 each being rigidly secured to a lower jaw portion 30 of each frame 10and die holders 24 each being supported by a hydraulic cylinder 32mounted in the upper jaw portion 34 of each frame 10 by bridging plates35 bolted thereto by bolts 37. Each die holder 24 is reciprocallyvertically movable relative to a fixed die holder 22 by rod 36.

Die holders 26 are rigidly secured to lower jaw portions 38 of movableC-frames 16 and die holders 28 are each supported by a hydrauliccylinder 40 mounted in the upper jaw portion 42 of each frame 16 byflange 43 and bolts 45. Die holders 26,28 thus are movable with eachmovable C-frame 16, each die holder 28 being reciprocally movablevertically relative to die holder 26 by rod 44.

Each of movable C-frames 16 is laterally reciprocal by a double-actinghigh-pressure forging cylinder 46 connected thereto by rod 47 such thatdie holders 26,28 can be extended to and retracted from opposed dieholders 22,24. Each forging cylinder 46 is mounted between a pair ofadjacent stationary C-frames 10 and secured thereto by bolts 48 throughflanges 49. A hydraulic system, well known in the art, supplies ahydraulic fluid uniformly to cylinders 46 such that all cylinders worktogether in unison, as will be described.

Die holders 22,24 interact to clamp a workpiece between upper and lowerjaw portions 34,30 of stationary C-frames 10 and die holders 26,28interact to clamp a workpiece between upper and lower jaw portions oflaterally reciprocal C-frames 16 for abutment of the workpieces togetherfor forge welding upon extension of forging cylinders 46.

Three detent cylinders 50 mounted on the lower jaw portions 30 ofstationary clamps 10 by bolts 52 through cylinder flanges 53 extendbetween certain stationary clamps 10 for abutment of guide pins 51against lower die holders 26 to positively space die holders 26 apredetermined parallel spaced distance from opposed stationary lower dieholders 22 whereby workpieces clamped between dies 22',24' and 26',28'respectively can be spaced apart to define an elongated open rectangularchannel 19 therebetween.

A segmented heater 54 extending the length of the lower dies 22',26' isdisposed in the cavity 56 formed below said lower dies and preferablysecured to stationary C-frame 10, as shown most clearly in FIGS. 5through 8, through die holder 22 or alternatively secured to die 22'.Heater 54 consists of a plurality of six inch burner segmentsinterconnected to form manifold 60 with outlets 58 equispaced at about1/8 inch intervals adjacent the length of the lower dies for introducinga uniform flow of a combustion mixture of gases to achieve uniformheating of the edges of workpieces clamped by the dies. A mixture ofoxygen and fuel gas such as propane has been found satisfactory toprovide heat requirements of about 5500° F. to achieve a workpiecetemperature of from about 200° to about 900° F.

Heater 54 is adapted by valving to provide heat at a predeterminedportion of the pressure welding cycle when the aforementionedrectangular channel is defined at a preset width between workpieces, asrepresented by the sequence of steps illustrated in FIG. 10.

We have found optimum heating and temperature control of workpieces canbe achieved by providing an air curtain designated by arrows 75 in FIG.7 between combustible gas outlets 58 and die 22' for deflection of theheating gases through the rectangular channel 19.

Referring now to FIG. 5, the air curtain is provided by a plurality ofjets of air discharged under pressure into cavity 56 from manifold 62extending parallel to heater manifold 60 through the outlets 64equispaced at a linear spacing of about 1/4 inch. Relative heating ofthe exposed edges of workpieces defining channel 19 can be controlled bypassing a desired volume of air between the source of heat from burneroutlets 58 and the workpiece edge carried by dies 22',24' such that saidedge is shielded from the heat supply permitting the opposed edge to beheated more rapidly. Equalization of the temperature of workpiece edgescan thus be attained when the workpiece carried by dies 22',24' isnormally heated to a higher temperature than the temperature of theworkpiece carried by dies 26',28' due to gas flows in cavity 56.Reduction of the edge temperature of the workpiece carried by dies22',24' relative to the temperature of the opposed workpiece may bedesired when the workpieces are of different thickness or when theworkpieces are of different alloy composition.

Cooling of the dies is provided by water passages in each of the upperand lower dies. A single passage 97,98 shown formed longitudinally ineach of upper dies 24',28' was found to return the dies to initial dietemperature of about 55° F. within 20 seconds of cessation of heatingand hence before initiation of the next heating cycle. A pair of waterpassages 100,102, shown formed longitudinally in each of lower dies22',26', in lieu of a single passage, can be provided if desired toaccelerate cooling of the dies.

Workpieces 11 illustrated in FIG. 9 may be formed by extrusion and eachworkpiece edge 66 has a nose configuration which comprises flattened tip68 and bevelled side faces 70 to provide a cross-section with materialthickness "T", root dimension "R", length dimension "L" and enddimension "E". We have found that a ratio of L:R of at least about1.1:1, preferably in the range of from about 1.1:1 to about 1.5:1, and aratio of E:R of at least about 0.4:1, in the range of from about 0.4:1to 1:1, preferably about 0.5:1, are important to obtain satisfactoryabutment of core material 72 with upset of surface oxides and softenedmetal as flash. Shoulders 86,88 formed on each workpiece for engagementby the dies can be formed, as shown, one or both shoulders spacedrearwardly remote from the nose of the workpiece, in which case R couldequal T, or formed on one side only of the workpiece.

Although it will be understood we are not bound by hypotheticalconsiderations, we believe the nose configuration aids rapid andcontrolled heating of workpiece edges to be pressure welded to provide atemperature gradient such that the heated edge tip 68 and side faces 70can be laterally deformed and upset, as shown with reference to FIGS. 6through 8 and FIG. 11, with abutment of cooler and harder inner corematerial 72 of each workpiece which has not had its mechanicalproperties adversely altered by the heat.

The steep temperature gradient provides a peripheral zone of plasticmaterial at relatively high temperature, i.e. up to about 800° F.,surrounding a core of harder material at lower temperature, i.e. up toabout 450° F. During the pressure welding process the harder corematerial functions as a "spear" and divides and expels the softoverheated material from the weld joint. The oxide layer coating theworkpieces thus is ruptured and expelled by extrusion with overheatedmaterial softened by annealing during the heating stage into the flashcavity as flash 71, to preferably increase the interface thickness atleast 1.6 times the cross-sectional area of the workpiece metal. Theminimum L:R ratio of 1.1:1 provides sufficient material upset for theformation of a strong weld under forging pressures unaffected bydeleterious materials. A ratio of L:R of greater than 1.5:1 would resultin the abutment and expulsion of excess harder core material 72 withresulting slippage of dies and inconsistency of weld uniformity. The E:Rratio range of from about 0.4:1 to 1:1, preferably about 0.5:1, providesthe desired steep temperature gradient illustrated in FIG. 9, withresultant desired flow characteristics shown in FIG. 11.

In operation, a shaped workpiece 11, having a longitudinal edge on eachside as shown most clearly in FIG. 9, is fed into machine cavity 13 fromthe side while the machine is in its open position, i.e. upper dieholders 24,28 are in their raised positions and the plurality oflaterally movable C-frames 16 have been retracted, to the left as viewedin FIG. 2. With reference to FIGS. 5 through 8, one workpiece 11 isclamped between die holders 22,24 of the stationary C-frames such thatshoulders 82,84 formed in dies 22',24', respectively, can engageshoulders 86,88 along one edge of workpiece 11. A second workpiece 11 isfed into cavity 13 to be clamped between die holders 26,28 of themovable C-frame 16 in like manner, shoulders 90,92 in dies 26',28'adapted to engage shoulders 86,88 along the opposed edge of theworkpiece.

Upper die holders 24,28 are lowered to clamp the two workpieces 11, asindicated in FIG. 6, under a light clamping cylinder pressure of 200-300psi and the opposed edges of the workpieces forced together under lightpressure of from about 200-500 psi of the forging cylinders to obtainalignment thereof relative to each other and to the forging dies. Thefinal cylinder clamping pressure of about 2200 psi, dependent on thenature of the metal welded and its thickness, is immediately applied tothe die holders and maintained to the completion of pressure welding.FIG. 10 illustrates graphically the steps of the method of our inventionwith reference to forging cylinder pressure, detent cylinder pressure,heat supply temperature and workpiece temperature. An increase offorging cylinder pressure will be noted during the positioning step ofthe cycle.

The detent cylinders 50 are then actuated at a pressure above 250 psisufficient for extension of guide pins 51, which function as stops inopposition to the forging cylinders, concurrent with reduction of theforging pressure, to space the workpieces a predetermined distance offrom 1/32 to 1 inch apart, preferably about 1/8 inch apart, to define anelongated open rectangular channel 19 shown most clearly in FIG. 7.

Control valves to heater 54 are then opened, by solenoids not shown, tointroduce a uniform flow of heating gases, such as oxygen and propaneignited by a pilot flame and combusted in situ, to rapidly heat theworkpiece nose configurations as shown in FIG. 9. Heating of theworkpieces has been found to take about 3 to 8 seconds for a metalworkpiece thickness of about 1/4 inch. Heat times in excess of 8 secondshave often resulted in loss of metal properties, inconsistent welds andapparent oxide inclusions at the weld joints. Heat times of about 4 to 6seconds have resulted in a consistent and level hardness profile throughthe weld section with no loss of properties.

Detent cylinder pressure is then released and, substantially concurrentwith cessation of heating of the workpieces, the forging pressure can beapplied to eliminate the heating channel and bring the workpieces intoabutment for about 2 to 5 seconds, normally about 3 seconds, withresultant pressure welding of the workpieces and simultaneous expulsionof flash 71 as shown in FIGS. 8 and 11.

The forging pressure is then relieved, cylinder 32 retracted to raiseupper die holder 24 and release the welded workpieces from front dies22',24', and the forging cylinders 46 and movable C-frames 16 connectedthereto partially retracted to separate dies 26',28' from dies 22',24'and to free the resulting panel from lower die 22'. Cylinder 32 is againactuated to pinch the panel between dies 22',24' while rear dies 26',28'are separated by retraction of upper die 28' by raising die holder 28through cylinder 40, and forging cylinders 46 then fully retracted tofree the panel from die 26'.

A walking beam table, not shown, raises the panel about one-half inchabove the lower dies 22',26' and partially draws the panel out of themachine so that the rearward edge of the panel can be pressure welded tothe next workpiece fed to the machine by a repeat of the forge weldingcycle.

It is essential for successful pressure welding that machine alignmentbe maintained throughout each welding cycle, i.e. the front and rearlower dies be maintained in the same horizontal plane, each of the pairsof rear upper and lower dies and the front upper and lower dies bemaintained in their respective vertical planes, and symmetry of diefaces be provided along the length of the machine. We have found the useof alignment rods 18 sliding within pillow blocks 17 effectively alignsthe front and rear lower dies in the same plane. Vertical alignment ofeach pair of upper and lower dies is provided by the configurations ofthe stationary and movable C-frames and symmetry of die faces is ensuredby abutment of front and rear dies with each other as indicated in FIG.8, or by abutment of lower die holders with each other, not shown.

Pressure welding of aluminum workpieces having "T" thicknesses of 0.140,0.210 and 0.220 inch thickness has been conducted successfully onaluminum alloys designated 6063-T6, 6061-T6, 6351-T6, 5456-H111,7005-T53 and 7075-T6 and, with the exception of 7075-T6, 100% jointefficiences have been obtained through the weld. Joint efficiency ofabout 90% was obtained for the 7075-T6 alloy and tests have indicated100% joint efficiency can be obtained for this alloy by increasing theforging capacity of the machine or reducing the cross section of theworkpiece.

Tests conducted on the workpiece shown most clearly in FIG. 9, extrudedfrom the aluminum alloy 6061-T6, with shoulders 86,88 formed thereon forengagement by the dies, as has been described, are exemplary of testsconducted on the aforementioned alloys. A shoulder 86,88 of 0.060 inchthickness on each side of the workpiece, to provide a resulting rootdimension R of 0.330 inch for material thickness T of 0.210 inch,resisted slippage of the workpieces in the dies and permittedsatisfactory welds. Optimum expulsion of flash 71 with removal of oxidesand of material heated over 500° F., as shown most clearly in FIG. 11,was obtained by a length dimension L of 0.375 inch and end dimension Eof 0.155 inch, providing an L:R ratio of 1.14:1 and an E:R ratio of0.47:1.

The present invention provides a number of important advantages.Workpieces of high strength aluminum or magnesium can be pressure weldedtogether by the method and apparatus of the invention to provide asolid-phase weld bond having physical characteristics substantiallyequal to the characteristics of the parent metal welded. Not only areundesirable effects from the use of excess heat from conventional forgewelding obviated, but weld strengths greater than the strength of theparent metals welded can be obtained. Heating and pressure welding ofworkpieces can be quickly effected in less than 10 seconds, with acomplete welding cycle, including assembly and alignment of workpiecesand removal of finished panel, taking place in about one-half minute.Complex extrusions of either open or closed sections, having suitablewelding edges, can be joined to form integral panels. Thus workpieces indesired shapes can be formed using relatively inexpensive extrusionpresses and a multiplicity of shaped workpieces quickly pressure weldedtogether to form continuous panels of desired length and structuralconfigurations without loss of physical properties of the parent metalwelded.

Panels formed of pressure welded aluminum extrusions have beensuccessfully incorporated in dump trailers and dump bodies to increaseload capacity by lowering vehicle weight.

It will be understood, of course, that modifications can be made in theembodiment of the invention illustrated and described herein withoutdeparting from the scope and purview of the invention as defined by theappended claims.

I claim:
 1. A forging press for joining two metal workpieces together bypressure welding comprising:(a) at least one pair of stationary C-shapedmetal plate frames arranged in a parallel side-by-side spaced-apartrelationship, (b) a laterally movable C-shaped metal frame mountedbetween each pair of stationary C-shaped metal plate frames, (c) a firstpair of die holders associated with each pair of stationary C-shapedmetal plate frames adapted to grip a workpiece therebetween, at leastone of said die holders being mounted for reciprocal movement in adirection towards and away from the other, (d) a second pair of dieholders associated with said laterally movable C-shaped metal frameadapted to grip a workpiece therebetween, at least one of said dieholders being mounted for reciprocal movement in a direction towards andaway from the other, (e) means for moving said laterally movableC-shaped metal frame between said stationary C-shaped metal plate framescomprising a double-acting forging cylinder rigidly secured to thestationary C-shaped metal plate frames and operatively connected to saidmovable C-shaped metal frame and a detent cylinder rigidly secured tosaid stationary C-shaped metal plate frames and operatively connected tosaid movable C-shaped metal frame in opposition to the forging cylinderwhereby die holders associated with said laterally movable C-shapedmetal frame can be moved towards and away from the die holdersassociated with said stationary C-shaped metal plate frames such thatworkpieces gripped therebetween can be spaced a predetermined distanceapart in alignment with each other prior to abutment of said workpiecesfor pressure welding and can be abutted together at a pressure above theyield strength of the parent material at working temperatures sufficientto permit metal flow, and (f) means for rapidly heating the opposededges of said workpieces to a uniform temperature within the range offrom about 200° to about 900° F. while said workpieces are spaced afixed distance apart immediately prior to abutment for pressure weldingincluding a heat source uniformly disposed along the spaced edges of theopposed workpieces comprising a manifold assembly disposed adjacent oneof said dies having a plurality of outlets disposed at equal intervalsalong the length of the said die adapted to introduce a flow of acombustible mixture of gases to achieve said uniform heating of theopposed edges of the workpieces.
 2. A press as claimed in claim 1 whichadditionally comprises means for introducing a curtain of air betweenthe heat source and adjacent die for directing the flow of heating gasestowards a rectangular channel defined between the opposed edges of theworkpieces.